Bounding Surface Model for Cyclic Biaxial Bending of RC Sections

Abstract

An incremental model is proposed for the nonlinear relationship between the normal action effects N, My, and Mz and the corresponding cross‐sectional deformations, εo,ϕy, and ϕz, of rectangular reinforced concrete cross sections. The incremental relationship is of the bounding‐surface plasticity type: The bounding surface of the cross section, which corresponds to ultimate strength, is constructed in the stress space of N‐My‐Mz, and the plastic moduli of the incremental flexibility or rigidity relation are functions of the distance of the current stress point from the bounding surface, along the current direction of incremental loading. The functional dependence of the bounding surface and of the plastic moduli on the amount and distribution of longitudinal and transverse steel is given, as well as the coupling terms between axial deformation and curvatures in the incremental flexibility relation. The simple hysteresis rules, which make the model applicable for arbitrary load paths in the N‐My‐Mz space, including reversals, are also given.